Electric blasting cap



Feb. 9 1926.

A. L. OLIVER ELECTRIC BLASTING CAP Filed May 2, 1925 ATTORNEY Patented Feb. 9, 1926.

UNITED STATES PATENT OFFICE..-

ALBERT LESLIE OLIVER, OF OAKLAND, CALIFORNIA, ASSIGN OR TO CALIFORNIA CAP COMPANY, OF OAKLAND, CALIFORNIA, A CORPORATION OF CALIFORNIA.

ELECTRIC BLASTING CAP.

Application filed May 2, 1925.

To all whom it may concern:

Be it known that I, ALBERT LESLIE OLIVER, a citizen of the United States, residing at Oakland, in the county of Alameda and State of California, have invented certain new and useful Improvements in Electric Blasting Caps, of which the following is a specification.

The present invention relates to electric blasting caps of the delay type, and constitutes an improvement upon the device for which Letters Patent of the United States No. 1378269 were issued on May 17, 1921, upon my application.

The objects of the present invention are, in general, similar to those expressed in said Patent No. 1378269, viz, to provide a delay blasting cap in which the filtering means, for preventing the issuance of sparks or flame, is formed as an integral part of the device, so that it cannot be separated therefrom, and to provide an effective filtering means to positively prevent the issuance of sparks or flame rior to the setting off of the detonating mem er, thereby eliminating the possibility of a premature blast.

The particular objects of the present improvements, however, are to provide a blasting cap of the type described which is entirely moisture-proof, and which will retain its advantages and effectiveness under all ordinary conditions of temperature. It is well suited, therefore, for use in gaseous places or in the presence ofeasily ignited explosives, under any conditions of weatheror temperature.

With the above and other objects in view, the invention consists in the novel construc tion and combination of parts hereinafter described, illustrated in the accompanying drawings, and set forth in the claim hereto appended, it being understood that the form, proportion and construction may be varied, within th limits of said claim, without departing from the spirit of the invention.

To comprehend the invention, reference is directed to the accompanyingdrawings, wherein- Fig. 1 is a longitudinal section of a blasting cap embodying the present invention in its preferred form. 4

Fig. 2 is an elevation of the vent sealing member before being applied to the body of the device.

Fig, 3 is a section taken on the line 3-3 Serial 1T0. 27,443.

of Fig. 1 and enlarged, showing the position of the vent sealing member during operation.

In the drawings, the reference numeral 1 designates a suitable time fuse of any desired length, having a powder train 2 extending from end to end therethrough. A detonating member 3, of any suitable and well known construction and material, is permanently secured, as at 4, to the lower end of the fuse 1, and is adapted to be set off by the flame propagated through the powder train 2. A sleeve 5 of suitable water proof material is preferably positioned to cover and protect the joint between the fuse 1 and the detonating member 3.

To the upper end'of the fuse 1 is secured a shell 6, preferably metalic, containing the igniting and filtering means, and the vent for the escape of the gases formed by the burning of the powder train 2. A suitable plug 7 of refractory material, preferably porcelain, is loosely fitted within said shell 6, and is spaced above the end of the fuse 1 as shown, providing an expansion chamber 8 for said gases. The lower face of the plug 7 is cupped, and contains a body of suitable inflammable material 9, such as priming powder, which has embedded in it an electric resistance unit 10. Insulated conductors 11, connected with the ends of said resistance unit, extend upwardly through the refractory plug 7, and out through the upper end of the shell 6. Therefore, when an electric current, from any suitable source not shown, is passed through the resistance unit 10, the priming powder 9 is ignited, and it in turn ignites the upper end of the powder train 2. The flame then travels through the fuse 1, finally reaching and exploding the detonator 3 after the required interval of time, such time interval being determined by the length of said fuse.

Within the shell 6 above the refractory plug 7 is a body of non-inflammable filtering material 12. Any suitable material may'be used at this point, but I prefer to employ either lead shot or silica sand of a definite diameter. Above the filtering material 12 is a sealing plug 13, preferably sulfur, for permanently closing the upper end of the shell 6. A felt or paper washer and a layer of sand, as shown respectively at 14 and 15, may be interposed between the filtering material and the sealing plug 13, to prevent the latter from running down into said filtering material when being poured into the shell in a molten state.

The shell 6 is provided, in its upper end region, with one or more vent apertures 16. In order to normally close said vents to prevent moisture from entering the shell 6 and affecting the priming powder 9 and the powder train 2, a sealing member 17 preferably comprising a strip of some suitable flexible water proof material, such for example as tin or lead foil, is wrapped around the outside of the shell 6, in such a position as to completely cover and close said vents. The sealing member 17 is preferably secured to the shell 6 by being cemented or otherwise joined thereto in the region of its edges, the cemented or adhering portion of said member extending around three of its edges as indicated by the shading 18 in Fig. 2. Thus when said member 17 is wrapped around the shell 6, with the cemented end 19 overlapping the noncemented end 20, as shown in Fig. 3, all "its exposed edges are firmly joined to said shell by the cement, thereby making a moisture proof seal or closure for the vents 16.

The central region of the sealing member 17' is preferably not joined to the shell -6. Therefore, when the gases formed by the burning of the priming powder 9 and the'powder train 2, passing up around the refractory plug 7 and through the filtering material 12, accumulate with sufficient pressure, they issue from the vents 16, bulging or expanding the free centralportion of the flexible seal member 17 away from the she I '6, as shown at 21 in Fig. 3, and finaly bursting said seal member, as shown at 22,

to permit their free escape. The effect of the bulging or expanding of the seal mem ber 17, as shown at 21 in Fig. 3, is to provide an additional expansion chamber for the gases, so that an appreciable time may elapse between the ignition of the priming powder 9 and the bursting of the said seal member. Such a lapse of time allows said gases to cool sufliciently to extinguish an sparks or flame which may have passed through the filtering material 12. After the burning of the priming powder 9, said filtering material is amply sufficient to extinguish any sparks result ng from the comparatively less violent and more remote burning of the powder train 2, but the provision of the expansion chamber 8 and the additional expansion space formed by the expanding orbulging of the free central portion of the flexible seal member 17 gives added security ag inst the issuance of sparks caused by the initial and more violent boring of the priming powder 9.

It will be'understood readily that the flexible seal member 17, properly cemented at its exposed edges, forms a closure for the vents 16 which 1s unaffected by either moisture or changes in temperature. Thus the device may be usedwith safety even in temperature below freezing, and under any conditions ordinarily met with in blasting operations:

I claim v A device for the described "purpose comprising a fuse; a detonating member associated with one end thereof; a closed shell fitted to the other end of said fuse, said shell having a 'vent in its wall; an inflammable substance within said shell for ignitin said .sheet having its exposed edges permanently joined to said shell, its central region being free to expand away from said shell before bursting.

In testimony whereof I have signed my name to this specification.

ALBERT LESL E OLIVER. 

